Molly actor Samuel Johnson has announced his retirement from acting after nearly 25 years to focus on cancer research.

Johnson’s announcement came only weeks after the Australian actor starred in the Seven Network’s two-part series Molly, which attracted more than 1.7 million viewers on its opening night.

The now-former actor and radio presenter announced on his charity’s Facebook page, Love Your Sister, that he would be hanging up his hat to focus on raising $10 million in the fight against cancer.

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“I can’t act anymore. Not if I’m to serve you properly,” Johnson said.

“I cannot play pretend on telly while our families are falling.

“Cancer is the last true riddle of our time (not of our doing) and I wanna be part of the push to solve it once and for all – part of the new ‘moonshot’.”

Johnson is known for travelling around Australia on a unicycle to raise funds for cancer research and to share the story of his sister Connie, who was first diagnosed with cancer at the age of 11.

The Underbelly actor said he could not play on television while “science is being murdered”.

“I promised that I would help raise $10 million for those brilliant bloody scientists and researchers at the Garvan Institute of Medical Research.”

He criticised the federal government’s lack of support to cancer research, describing federal funding as “static”.

“Not until we get to that $10 million and show those faceless f***ers at the top end of town just how serious we are about research here at ground level.”

Johnson said if it wasn’t for his role as Molly Meldrum in the mini series, he would have retired from acting earlier.

“I love acting, it’s the best job in the world,” he said.

“But the thing is, being a ‘vollie’ for healthy families kinda wins hands down. No contest.

“If it weren’t for Molly, I’d have done it sooner.”

Despite the announcement, Johnson admitted he will still have to do the odd voice-over “so I can eat if that’s okay!”